Organic light-emitting diode display with reduced lateral leakage

ABSTRACT

A display may have an array of pixels. Each pixel may have a light-emitting diode that emits light under control of a drive transistor. The organic light-emitting diodes may have a common cathode layer, a common electron layer, individual red, green, and blue emissive layers, a common hole layer, and individual anodes. The hole layer may have a hole injection layer stacked with a hole transport layer. Pixel circuits for controlling the diodes may be formed from a layer of thin-film transistor circuitry on a substrate. A planarization layer may cover the thin-film transistor layer. Lateral leakage current between adjacent diodes can be blocked by shorting the common hole layer to a metal line such as a bias electrode that is separate from the anodes. The metal line may be laterally interposed between adjacent pixels and may be formed on the planarization layer or embedded within the planarization layer.

This application claims the benefit of provisional patent applicationNo. 62/017,096 filed on Jun. 25, 2014, which is hereby incorporated byreference herein in its entirety.

BACKGROUND

This relates generally to electronic devices with displays and, moreparticularly, to displays such as organic-light-emitting diode displays.

Electronic devices often include displays. For example, cellulartelephones and portable computers include displays for presentinginformation to users.

Displays such as organic light-emitting diode displays have arrays ofpixels based on light-emitting diodes. In this type of display, eachpixel includes a light-emitting diode and thin-film transistors forcontrolling application of a signal to the light-emitting diode toproduce light. The light-emitting diodes may be provided with emissivematerials of different colors to create color images The emissivematerials may, for example, include red emissive material for formingred diodes in red pixels, green emissive material for forming greendiodes in green pixels, and blue emissive material for forming bluediodes in blue pixels.

During fabrication, some of the layers of material that are used informing the organic light-emitting diodes are deposited in the form ofblanket films that cover the entire display. For example, a display mayinclude a common hole layer formed from a blanket hole injection layerstacked with a blanket hole transport layer. Due to doping levels in thehole layer, it is possible for currents to leak laterally betweenadjacent pixels during operation of a display. For example, when a bluediode is being turned on and an adjacent red diode is being turned off,there is a potential for leakage current to laterally flow in the holelayer between an anode in the blue diode and an anode in the red diode.This can cause the red diode to turn on inadvertently.

It would therefore be desirable to be able to provide displays such asorganic light-emitting diode displays that exhibit reduced lateralleakage currents.

SUMMARY

A display may have an array of organic light-emitting diode pixels. Eachpixel may have a light-emitting diode that emits light under control ofa drive transistor. The organic light-emitting diodes may have a commoncathode layer, a common electron layer, individual red, green, and blueemissive layers, a common hole layer, and individual anodes. The commonhole layer may have a hole injection layer stacked with a hole transportlayer.

Pixel circuits for controlling the drive transistors may be formed froma layer of thin-film transistor circuitry on a substrate. Aplanarization layer may cover the thin-film transistor layer. Lateralleakage current between adjacent diodes can be blocked by shorting thecommon hole layer to a metal line such as a bias path that is separatefrom the anodes. The bias path may be laterally interposed betweenadjacent pixels and may be formed on the planarization layer or embeddedwithin the planarization layer.

During operation, the anodes may be driven at positive voltages and thecathode layer may be maintained at a ground voltage. The bias path maybe maintained at a voltage less than the ground voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an illustrative display such as an organiclight-emitting diode display having an array of organic light-emittingdiode display pixels in accordance with an embodiment.

FIG. 2 is a diagram of an illustrative organic light-emitting diodedisplay pixel of the type that may be used in a display in accordancewith an embodiment.

FIG. 3 is a cross-sectional side view of an illustrative organiclight-emitting diode display in accordance with an embodiment.

FIG. 4 is a top view of a set of pixels in an organic light-emittingdiode display in accordance with an embodiment.

FIG. 5 is a cross-sectional side view of another illustrative organiclight-emitting diode display in accordance with an embodiment.

DETAILED DESCRIPTION

A display in an electronic device may be provided with driver circuitryfor displaying images on an array of pixels. An illustrative display isshown in FIG. 1. As shown in FIG. 1, display 14 may have one or morelayers such as substrate 24. Layers such as substrate 24 may be formedfrom planar rectangular layers of material such as planar glass layers.Display 14 may have an array of pixels 22 for displaying images for auser. The array of pixels 22 may be formed from rows and columns ofpixel structures on substrate 24. These structures may include thin-filmtransistors such as polysilicon thin-film transistors, semiconductingoxide thin-film transistors, etc. There may be any suitable number ofrows and columns in the array of pixels 22 (e.g., ten or more, onehundred or more, or one thousand or more).

Display driver circuitry such as one or more display driver integratedcircuits may be coupled to conductive paths such as metal traces onsubstrate 24 using solder or conductive adhesive. Display drivercircuits such as display driver integrated circuit 16 may containcommunications circuitry for communicating with system control circuitryover path 25. Path 25 may be formed from traces on a flexible printedcircuit or other cable. The control circuitry may be located on a mainlogic board in an electronic device such as a cellular telephone,computer, television, set-top box, media player, portable electronicdevice, or other electronic equipment in which display 14 is being used.During operation, the control circuitry may supply display driverintegrated circuit 16 with information on images to be displayed ondisplay 14. To display the images on display pixels 22, display driverintegrated circuit 16 may supply clock signals and other control signalsto display driver circuitry such as row driver circuitry 18 and columndriver circuitry 20. Row driver circuitry 18 and/or column drivercircuitry 20 may be formed from one or more integrated circuits and/orone or more thin-film transistor circuits.

Row driver circuitry 18 may be located on the left and right edges ofdisplay 14, on only a single edge of display 14, or elsewhere in display14. During operation, row driver circuitry 18 may provide row controlsignals on horizontal lines 28 (sometimes referred to as row lines orscan lines). Row driver circuitry may sometimes be referred to as scanline driver circuitry or gate line driver circuitry.

Column driver circuitry 20 may be used to provide data signals D fromdisplay driver integrated circuit 16 onto a plurality of correspondingvertical lines 26. Column driver circuitry 20 may sometimes be referredto as data line driver circuitry or source driver circuitry. Verticallines 26 are sometimes referred to as data lines. During compensationoperations, column driver circuitry 20 may use vertical lines 26 tosupply a reference voltage. During programming operations, display datais loaded into display pixels 22 using lines 26.

Each data line 26 is associated with a respective column of displaypixels 22. Sets of horizontal signal lines 28 run horizontally throughdisplay 14. Each set of horizontal signal lines 28 is associated with arespective row of display pixels 22. The number of horizontal signallines in each row is determined by the number of transistors in thepixels 22 that are being controlled independently by the horizontalsignal lines. Display pixels of different configurations may be operatedby different numbers of scan lines.

Row driver circuitry 18 may assert control signals such as scan signalson the row lines 28 in display 14. For example, driver circuitry 18 mayreceive clock signals and other control signals from display driverintegrated circuit 16 and may, in response to the received signals,assert scan signals and an emission signal in each row of display pixels22. Rows of display pixels 22 may be processed in sequence, withprocessing for each frame of image data starting at the top of the arrayof display pixels and ending at the bottom of the array (as an example).While the scan lines in a row are being asserted, control signals anddata signals that are provided to column driver circuitry 20 bycircuitry 16 direct circuitry 20 to demultiplex and drive associateddata signals D onto data lines 26 so that the display pixels in the rowwill be programmed with the display data appearing on the data lines D.The display pixels can then display the loaded display data.

Each pixel in an organic light-emitting diode display contains arespective organic light-emitting diode. A schematic diagram of anillustrative organic light-emitting diode pixel is shown in FIG. 2. Asshown in FIG. 2, pixel 22 includes light-emitting diode 30. A positivepower supply voltage Vddel may be supplied to positive power supplyterminal 34 and a ground power supply voltage Vssel may be supplied toground power supply terminal 36. The state of drive transistor TDcontrols the amount of current flowing through diode 30 and thereforethe amount of emitted light 40 from pixel 22. Terminal 36 of diode 22represents the cathode of diode 22. A blanket cathode layer may be usedin display 14. The blanket cathode layer may overlap all of the pixelsin display 14 (i.e., the cathode layer may be a layer that is shared byall pixels 22). The use of a common cathode layer in display 14 may helpsimplify fabrication. In addition to having a cathode, each diode 30 hasa separate anode such as anode 42. Each anode in display 14 may beindependently controlled, so that each diode 30 in display 14 can beindependently controlled. This allows each pixel 22 to produce anindependently controlled amount of light 40.

Display pixel 22 may have storage capacitors Cst1 and Cst2 and one ormore transistors that are used as switches such as transistors SW1, SW2,and SW3. Signal EM and scan signals SCAN1 and SCAN2 are provided to arow of display pixels 22 using row lines 28. Data D is provided to acolumn of display pixels 22 via data lines 26.

Signal EN is used to control the operation of emission transistor SW3.Transistor SW1 is used to apply the voltage of data line 26 to node A,which is connected to the gate of drive transistor TD. Transistor SW2 isused to apply a direct current (DC) bias voltage Vini to node B forcircuit initialization during compensation operations. Bias voltage Vinimay be distributed across display 14 using paths such as bias voltagepath 44. Bias voltage Vini may be −4.4 volts or other suitable voltage(e.g., a voltage lower than the ground voltage on the cathode).

During compensation operation, display pixels 22 are compensated forpixel-to-pixel variations such as transistor threshold voltagevariations. The compensation period includes an initialization phase anda threshold voltage generation phase. Following compensation (i.e.,after the compensation operations of the compensation period have beencompleted), data is loaded into the display pixels. The data loadingprocess, which is sometimes referred to as data programming, takes placeduring a programming period. In a color display, programming may involvedemultiplexing data and loading demultiplexed data into red, green, andblue pixels.

Following compensation and programming (i.e., after expiration of acompensation and programming period), the display pixels of the row maybe used to emit light. The period of time during which the displaypixels are being used to emit light (i.e., the time during whichlight-emitting diodes 30 emit light 40) is sometimes referred to as anemission period.

During the initialization phase, circuitry 18 asserts SCAN1 and SCAN2(i.e., SCAN1 and SCAN2 are taken high). This turns on transistors SW1and SW2 so that reference voltage signal Vref and initialization voltagesignal Vini are applied to nodes A and B, respectively. During thethreshold voltage generation phase of the compensation period, signal EMis asserted and switch SW3 is turned on so that current flows throughdrive transistor TD to charge up the capacitance at node B. As thevoltage at node B increases, the current through drive transistor TDwill be reduced because the gate-source voltage Vgs of drive transistorTD will approach the threshold voltage Vt of drive transistor TD. Thevoltage at node B will therefore go to Vref-Vt. After compensation(i.e., after initialization and threshold voltage generation), data isprogrammed into the compensated display pixels. During programming,emission transistor SW3 is turned off by deasserting signal EM and adesired data voltage D is applied to node A using data line 26. Thevoltage at node A after programming is display data voltage Vdata. Thevoltage at node B rises because of coupling with node A. In particular,the voltage at node B is taken to Vref-Vt+(Vdata-Vref)*K, where K isequal to Cst1/(Cst1+Cst2+Coled), where Coled is the capacitanceassociated with diode 30.

After compensation and programming operations have been completed, thedisplay driver circuitry of display 14 places the compensated andprogrammed display pixels into the emission mode (i.e., the emissionperiod is commenced). During emission, signal EM is asserted for eachcompensated and programmed display pixel to turn on transistor EM3. Thevoltage at node B goes to Voled, the voltage associated with diode 30.The voltage at node A goes to Vdata+(Voled−(Vref-Vt)−(Vdata-Vref)*K. Thevalue of Vgs-Vt for the drive transistor is equal to the differencebetween the voltage Va of node A and the voltage Vb of node B. The valueof Va-Vb is (Vdata-Vref)*(1-K), which is independent of Vt. Accordingly,each pixel 22 has been compensated for threshold voltage variations sothat the amount of light 40 that is emitted by each of the pixels 22 inthe row is proportional only to the magnitude of the data signal D foreach of those pixels.

Each diode 30 in display 14 has layers of material interposed betweencathode 36 and anode 42. These layers may include a hole layer (e.g., ahole injection layer and a hole transport layer), an electron layer(e.g., an electron injection layer and an electron transport layer), alayer of emissive material (e.g., organic electroluminescent material),and optionally one or more additional layers of material. The emissivematerial may be different for the diodes for pixels of different colors.For example, red diodes may have red emissive material, green diodes mayhave green emissive material, and blue diodes may have blue emissivematerial. Because the diodes associated with pixels of different colorscontain emissive layers of different colors, separate evaporation masksare used to deposit the emissive material of each color. To simplifyfabrication, the hole layer and the electron layer may be deposited asblanket films that are common to all diodes in display 14.

The anode of each diode is separate, but the presence of common diodelayers such as the common hole layer serves as a potential path forlateral leakage currents between adjacent diodes. Lateral leakagecurrents can be suppressed by providing a path that sinks lateralleakage currents. The path that sinks the leakage currents can be formedfrom one of the conductive paths associated with operating pixels 22. Asan example, a conductive path such as bias voltage path 44 (FIG. 2) mayserve as a lateral leakage current sinking path. Bias voltage path 44may have a voltage (e.g., a negative voltage) that draws laterallyflowing leakage current downward out of the hole layer and therebyprevents the laterally flowing leakage current from disrupting operationof the diodes in adjacent pixels.

A cross-sectional side view of illustrative structures that may be usedin forming diodes 30 is shown in FIG. 3. Numerous diodes 30 are used informing display 14. Two illustrative adjacent pixels and two associateddiodes are shown in FIG. 3. Red pixel 22R is based on red diode 30R.Blue pixel 22B is based on blue diode 30B. Thin-film transistorcircuitry 52 (see, e.g., the pixel circuitry of FIG. 2) is formed onsubstrate 50. Substrate 50 may be a layer of glass, plastic, or othermaterial. Thin-film transistor circuitry 52 may be based on siliconthin-film transistors, indium gallium zinc oxide transistors or othersemiconducting oxide transistors, or other thin-film transistorcircuitry.

Thin-film transistor circuitry 52 may include drive transistors TDR andTDB (e.g., drive transistors such as drive transistor TD of FIG. 2).Drive transistor TDR is used to supply current to anode 58R of red diode30R. Drive transistor TDB is used to supply current to anode 58B of bluediode 30B. Transistor TDR has terminals such as source-drain terminals54R and gate terminal 80R. Transistor TDB has terminals such assource-drain terminals 54B and gate terminal 80B.

Dielectric planarization layer 56 may cover transistors such astransistors TDR and TBD in thin-film transistor circuitry 52.Planarization layer 56 may include a layer of inorganic material (e.g.,silicon nitride) covered with a layer of polymer material (e.g.,photoimageable polymer such as photoimageable acrylic) or otherdielectric materials.

Anode 58R for red diode 30R and anode 58B for blue diode 30B may beformed on the surface of planarization layer 56. Openings inplanarization layer 56 allow anodes 58R and 58B to be shorted tosource-drain terminals 54R and 54B in transistors TDR and TDB,respectively. A conductive layer such as a layer of metal or otherconductive material may be used in forming anodes 58R and 58B. Theconductive layer may be patterned to form separate anodes for the diodesof pixels 22 such as anodes 58R and 58B. Portions of the conductivelayer such as portion 60 may also be used to form a current sinkstructure that draws away lateral leakage current from the red and bluediodes. In the illustrative arrangement of FIG. 3, current sink path 60has been formed from part of the same conductive layer that is used informing anodes 58R and 58B. Path 60 may be shorted to bias voltage Vinion path 44 of FIG. 2 (i.e., path 60 of FIG. 3 may form part of path 44of FIG. 2).

Red diode 30R of red pixel 22R has red emissive layer 66R. Blue diode30B of blue pixel 22B has blue emissive layer 66B. The red emissivematerial of layer 66R and the blue emissive material of layer 66B arepreferably separate from each other. During fabrication, layer 66R andlayer 66B may be deposited by evaporating separate red and blue emissivematerials through respective red and blue masks. Green emissive material(not shown in FIG. 3) is deposited through a mask in alignment with adrive transistor and diode structures for a green diode in a greenpixel. The use of separate masks to deposit layers 66R and 66B allowsthe emissive materials for the red and blue diodes to be patternedseparately, but adds process complexity.

To help minimize process complexity, the diode layers other than thecolored emissive layers are preferably deposited using blanket layers ofmaterial (e.g., layers of material that are common to the diodes of allpixels 22 and that cover all of display 14). As shown in FIG. 3, forexample, display 14 may have blanket (common) layers such as common holelayer 64 under emissive layers 66R and 66B, common electron layer 68covering the emissive layers, and common cathode layer 70. Cathode layer70 forms a common cathode terminal (see, e.g., cathode terminal 36 ofFIG. 2) for all diodes in display 14. Cathode layer 70 may be formedform a transparent conductive material (e.g., indium tin oxide, a metallayer(s) that is sufficiently thin to be transparent, a combination of athin metal and indium tin oxide, etc.). Electron layer 68 may includelayers such as an electron injection layer and electron transport layer.Hole layer 64 may include layers such as a hole injection layer and ahole transport layer.

Pixel definition layer 62 may be formed on top of planarization layer56. Pixel definition layer 62 may be formed from a polymer such as blackphotoimageable polyimide or other polymer. Pixel definition layer 62 maybe formed on top of the anode layer (e.g., anodes 58R and 58B, and biasvoltage conductor 60). Openings may be formed in pixel definition layer62 to allow the common layers to contact anodes 58R and 58B. Forexample, in pixel 22R, pixel definition layer 62 may have opening 72R toallow electron layer 64 and the layers stacked above layer 64 to contactanode 58R. During operation of red pixel 22R, current flows from anode58R vertically upwards through the stacked layers of diode 30R tocathode 70. Similarly, in pixel 22B, pixel definition layer 62 may haveopening 72B to allow electron layer 64 and the layers stacked abovelayer 64 to contact anode 58B. During operation of blue pixel 22B,current flows from anode 58B vertically upwards through the stackedlayers of diode 30B to cathode 70.

Ideally, adjacent diodes 30 in display 14 such as diodes 30R and 30B ofFIG. 3 operate independently. In practice, the presence of common layerssuch as hole layer 64 present an opportunity for leakage current fromone diode to flow laterally into an adjacent diode, thereby potentiallydisrupting the adjacent diode. For example, there is a possibility thatthe process of applying a drive current to the blue diode between anode58B and cathode 70 in blue pixel 22B will give rise to lateral leakagecurrent through layer 64 (e.g., a current from anode 58B to anode 58R)that could enter diode 30R of red pixel 22R and thereby inadvertentlyturn on the red diode and create light in the red pixel. This potentialfor interference between adjacent diodes can be reduced or eliminated byshorting hole layer 64 to bias path (electrode) 60 though portion 74 ofhole layer 64.

The drive voltages on the anodes of display 14 may, as an example, rangefrom about 2 volts (when a given pixel is dark) to 5 volts (when a givenpixel is driven at its maximum intensity). Bias voltage Vini on biaspath 60 may, as an example, have a negative voltage such as a voltage of−4.4 volts (or other suitable voltage level). Cathode 70 may bemaintained at a voltage of 0 volts or other suitable ground voltage.

In this type of configuration, bias path (bias voltage path) 60 canblock lateral leakage currents. In particular, when bias path 60 islaterally interposed between adjacent anodes such as anodes 58R and 58B,any leakage current that is flowing in hole layer 64 from anode 58B willbe drawn downward into bias path 60 (due to the negative voltage of path60), rather than continuing laterally into the adjacent diode (which isat 2 volts or higher). For example, lateral leakage current 78 fromanode 58B in blue diode 30B may be drawn into bias path 60 when bluediode 30B is being operated and lateral leakage current 78 from anode58R in red diode 30R may be drawn into bias path 60 when red diode 30Ris being operated.

A top view of a set of red, blue, and green pixels 22 for display 14 isshown in FIG. 4. The set of pixels shown in FIG. 4 may be tiled acrossthe surface of display 14 (i.e., the set of pixels may be arranged inrows and columns as shown in FIG. 1). Bias path 44 may have a gridpattern including portions that surround each set of red, blue, andgreen pixels, as shown in FIG. 4. To block lateral leakage currents thatmay disrupt the operation of adjacent pixels, at least some portions ofbias path 44 extend between adjacent pixels. Portion 60 of bias path 44may, for example, be interposed between blue pixel 22B and red pixel22R, as shown in FIG. 4. FIG. 3 is a cross-sectional side view ofdisplay 14 of FIG. 4 taken along line 82 and viewed in direction 84. Asdescribed in connection with the cross section of FIG. 3, the presenceof a current sink path such as bias path 60 between anode 58B of bluepixel 22B and anode 58R of red pixel 22R draws lateral leakage current78 from blue diode 30B into path 60 and draws lateral leakage current 76from red diode 30R into path 60. The presence of path 60 therefore helpsisolate the blue and red pixels of FIG. 4.

Red pixels may be particularly sensitive to interference from adjacentpixel leakage and blue pixels tend to be driven strongly, so, ifdesired, path 60 between adjacent red and blue pixels may be the onlyisolation path that is formed. If desired, additional isolation pathextensions to bias path 44 may be formed. For example, path 60″ may beformed between green pixel 22G and red pixel 22R to isolate the greenand red pixels from each other and path 60′ may be formed between bluepixel 22B and green pixel 22G to isolate the blue and green pixels fromeach other. In displays with pixels of other colors, additionalisolation paths may be formed. The configuration of FIG. 4 in which thered and blue pixels are isolated using path 60 is merely illustrative.

If desired, isolation path 60 may be formed using a layer of metal thatis embedded within planarization layer 56, as shown in FIG. 5. This typeof arrangement may make it possible to enhance the aperture ratio forpixels 22, because the placement of path 60 within layer 56 allows anodespacing to be minimized. As shown in FIG. 5, planarization layer 56 mayhave a first dielectric layer such as dielectric layer 56A and a seconddielectric layer such as dielectric layer 56B. Layer 56A may be aninorganic dielectric layer such as a layer of silicon nitride or may beother suitable dielectric. Layer 56B may be an organic dielectric layersuch as a layer of photoimageable acrylic or other suitable dielectric.During fabrication, a metal layer may be deposited and patterned onlayer 56A to form isolation path 60 and other portions of bias path 44(FIGS. 2 and 4). Layer 56B may then be deposited, thereby embedding path60 within the dielectric material of planarization layer 56.Planarization layer 56 can be patterned before or after deposition ofpixel definition layer and the formation of opening 721 in pixeldefinition layer to form an opening for portion 74 of hole layer 64.After depositing layers 64, emissive layers 66R and 66B, layer 68, andlayer 70, portion 74 will contact path 60 and short layer 64 to path 60,as described in connection with FIG. 3.

The foregoing is merely illustrative and various modifications can bemade by those skilled in the art without departing from the scope andspirit of the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. A display comprising: an array of pixels, eachpixel having a respective organic light-emitting diode and a pixelcircuit, wherein the pixel circuits include a bias path and wherein aportion of the bias path is interposed between first and second pixels;a common hole layer that forms part of each of the organiclight-emitting diodes in the array of pixels; and a pixel definitionlayer having an opening through which the common hole layer is shortedto the portion of the bias path that is interposed between the first andsecond pixels.
 2. The display defined in claim 1 wherein the common holelayer comprises a hole injection layer and a hole transport layer. 3.The display defined in claim 2 wherein the first pixel comprises a redpixel and wherein the second pixel comprises a blue pixel.
 4. Thedisplay defined in claim 3 wherein the red pixel and blue pixel haverespective anodes and wherein the bias path comprises a portion of alayer of material that forms the anodes.
 5. The display defined in claim4 further comprising: a substrate; and thin-film transistor circuitryfor the pixel circuits, wherein the thin-film transistor circuitry isformed on the substrate.
 6. The display defined in claim 5 furthercomprising: a dielectric layer on the thin-film transistor circuitry,wherein the anodes and the bias path are formed on the dielectric layer.7. The display defined in claim 6 wherein the organic light-emittingdiodes have a common cathode that is maintained at a first voltage andwherein the bias path is maintained at a second voltage that is lessthan the first voltage.
 8. The display defined in claim 3 wherein thered pixel and blue pixel have respective anodes formed from a layer ofmaterial and wherein the bias path comprises a portion of a layer ofmaterial other than the layer of material that forms the anodes.
 9. Thedisplay defined in claim 3 further comprising: a substrate; thin-filmtransistor circuitry for the pixel circuits, wherein the thin-filmtransistor circuitry is formed on the substrate; and a dielectric layeron the thin-film transistor circuitry, wherein the anodes are formed ona surface of the dielectric layer and wherein the bias path is embeddedwithin the dielectric layer.
 10. The display defined in claim 9 whereinthe organic light-emitting diodes have a common cathode that ismaintained at a first voltage and wherein the bias path is maintained ata second voltage that is less than the first voltage.
 11. The displaydefined in claim 2 wherein each organic light-emitting diode has anemissive layer on the hole layer.
 12. The display defined in claim 11wherein the emissive layers include red emissive layers, green emissivelayers, and blue emissive layers.
 13. The display defined in claim 12wherein the organic light-emitting diodes share a common electron layerthat has an electron injection layer and an electron transport layer andwherein the emissive layer of each organic light-emitting diode isinterposed between the common electron layer and the common hole layer.14. The display defined in claim 2 wherein the bias path is coupled toan anode through a transistor.
 15. An organic light-emitting diodedisplay comprising: organic light-emitting diodes having a commoncathode layer, a common electron layer, and a common hole layer; anodeseach of which is associated with a respective one of the organiclight-emitting diodes; and a metal path in contact with the common holelayer, wherein a portion of the metal path is laterally interposedbetween first and second adjacent diodes in the organic light-emittingdiodes.
 16. The organic light-emitting diode display defined in claim 15wherein the first and second adjacent diodes have first and secondrespective anodes, wherein the display comprises a dielectric layer,wherein the first and second anodes are formed on the dielectric layer,and wherein the metal path is formed on the dielectric layer between thefirst and second anodes.
 17. The organic light-emitting diode displaydefined in claim 15 wherein the first and second adjacent diodes havefirst and second respective anodes, wherein the display comprises adielectric layer, wherein the first and second anodes are formed on thedielectric layer, and wherein the metal path is embedded within thedielectric layer at a location that is laterally interposed between thefirst and second anodes.
 18. The organic light-emitting diode displaydefined in claim 15 wherein the organic light-emitting diodes include aplurality of sets of light-emitting diodes each of which has a reddiode, a blue diode, and a green diode and wherein the metal path isinterposed between a red diode and a blue diode in a given one of thesets of light-emitting diodes and does not have any portions interposedbetween the green diode and the blue diode in that given set.
 19. Anorganic light-emitting diode display comprising: a plurality of organiclight-emitting diodes having a common cathode layer, a common electronlayer, a common hole layer, and respective individual anodes; and ametal structure shorted to the common hole layer that prevents lateralleakage current from flowing between first and second diodes in theplurality of organic light-emitting diodes by sinking the lateralleakage current.
 20. The organic light-emitting diode display defined inclaim 19 wherein the plurality of organic light-emitting diodes includered diodes having red emissive layers between the common electron layerand the common hole layer, green diodes having green emissive layersbetween the common electron layer and the common hole layer, and bluediodes having blue emissive layers between the common electron layer andthe common hole layer and wherein the first diode is one of the reddiodes and the second diode is one of the blue diodes.